Astronomers have confirmed the full size of IC 1101, the largest known galaxy, and it is wider than 17 Milky Ways lined up in a row.

The galaxy’s diameter is estimated at 520 kiloparsecs, or nearly 1.7 million light-years. Its stars add up to roughly 3.4 trillion solar masses. The measurements come from the deepest images ever taken of IC 1101, captured in 2022 by the Isaac Newton Telescope in the Canary Islands.

The study, submitted in July to the journal Astronomy and Astrophysics, identified the galaxy’s faint edge for the first time. Earlier estimates had put its width at about 370,000 light-years.

IC 1101 sits over a billion light-years away at the heart of the Abell 2029 galaxy cluster. It is still growing: tail-like features at its edges suggest it is merging with smaller galaxies, a process called galactic cannibalism.

Its core hosts a supermassive black hole estimated at 40 to 70 billion times the Sun’s mass, among the largest known.